Our actual fuel burn (Lehman 120s)

Where I live there is always current issues
To measure fuel burn /speed I reverse course 180 and average it out
That works for shorter distances

Done that. Most recently 1500 RPM netted 6 knots.

My 2K RPM translates into 7 knots over water and I've seen anywhere from 3.8 to 9 knots over land, depending on current and wind.

From the looks of your wake Mark I know your'e push'in more than 6 knots when you took that picture. You've posted so many pics I have the feeling you can't make a post without putting up some kind of picture. But the picture should be relevant to the text do you suppose? My keyboard feels critical this morning .. no offense.

But I love pictures so I shouldn't be complaining about pics at all.

Eric, that wake photo was taken when the Coot was moving nearly 6.5 knots through the water on a calm day. Don't have one at 6 knots and didn't think anyone could discern the difference. Note the line of waves and the change in angle where there was a current differential.

markpierce said:

Note the line of waves and the change in angle where there was a current differential.

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Last time it was posted the reason was water depth.

manyboats said:

............. You've posted so many pics I have the feeling you can't make a post without putting up some kind of picture. ............

Click to expand...

Well, they say a picture is worth a thousand words (a "kiloword") so think of all the typing he saves. Not to mention bandwidth.

rwidman said:

Well, they say a picture is worth a thousand words (a "kiloword") so think of all the typing he saves. Not to mention bandwidth.

Click to expand...

It might be worth reviewing your math ... a thousand words is about 16KB, one of Mark's pics is close to 200KB.

It might be worth the bandwidth if it were in context but a picture of a bergy bit taken from a cruise ship in some unknown location in a thread by and about a member's photos of his voyage south seems like a bit too much "me too" for good taste.

RickB said:

It might be worth reviewing your math ... a thousand words is about 16KB, one of Mark's pics is close to 200KB.

It might be worth the bandwidth if it were in context but a picture of a bergy bit taken from a cruise ship in some unknown location in a thread by and about a member's photos of his voyage south seems like a bit too much "me too" for good taste.

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Rick, sometimes your posts are true words of wisdon. Other times, such as this post, and the last one on the seacock handles, they are just useless blabbering.

A great example of wasted bandwidth.

RickB said:

Last time it was posted the reason was water depth.

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I subsequently came to a new hypothesis that it had to do with the varying current strengths in the body of water under observation. Nevertheless, tidal currents are subject to water depth where deeper water channels flow faster than in the shallows. (Faster waters scour the bottom, slower waters drop silt.)

OK Mark,
I zoomed in on it and it does look more like 6 knots ... well you say 6.5. I was thinking my Willy dosn't make that defined/steep a wake at 6.15 knots but that's the better part of 1/2 a knot and the Coot has considerably more wave-making resistance/ability that the Willard. With slow boats I've got a good eye for this though but sometimes I over look significant factors like a the inside bow wave in a slight turn. Your Coot w a much fuller bow, more power applied and a bit more speed should definitely make a bit more wake than a Willard 30.
So I was fooled into thinking you were going faster than you said. Sorry.

Ron,
I read your trip story. Soo many gators. I've never traveled that laid back and should take your lead and make a point of doing it. I just like being underway ... I think.lots of rivers and I like rivers but Willy is a bit too deep for depths under 5 or 6'. Studied the pics and have a start on my geography lesson .... thanks.

Eric, I think it's mostly about your Willard having a more efficient (as in more sailboat-like) hull shape than the workboat Coot with its fat butt and broad bow.

Oooh you are naughty Rick.
Actually, talking Lehman fuel use, I wished I had a flo-scan on Sunday. We were taking a friend who had helped me with a boat repair and his family, as a way of returning the favour, out to a special Celtic Festival lunch at a local waterside tavern. (Harrigans @ Calypso Bay) There was a forecast for strong winds, so we normally would have stayed at home, but because there was no danger at all in our sheltered bay channels, and we could not reschedule we still went, even though the wind was gusting to 35 knots at times. It did make the tying up at the tavern's pontoon a bit challenging but no dramas were encountered. On the way back with wind, waves and tide coming from behind, we were chortling along at 7.8 kn at little above fast idle - ie 1500 rpm. It would have been interesting to know what the burn was at that time. Kinda making up for when one is bashing into it.

I don't think it works that way Peter. But it may.

Consider an airplane going on a short flight. Climb to a fairly high altitude at WOT and sorta glide down to it's destination. Probably not a good analogy as air density screws it up.

How-a bout a truck going over hills continuously ... WOT about half the time and coasting down the hills the other half. I think a truck going the same distance on level ground would burn less fuel. You could say boats don't go up hills but winds as in Peter's trip would be the same as going up and down hills.

Any more opinions?

Sure Peter is correct...there are variables ....but going one way into it is often compensated for by going with it at some point.

Over simplified...but good enough/close enough until you get to relatively extreme conditions.

"but going one way into it is often compensated for by going with it at some point."

To me the question is to what extent.

I don't see how bucking wind and then going w it could work out to be a plus. But if there was no current and the wind was the same going both ways at the same speed it would seem to average out. If one went the same speed the resistance of the boat would remain the same below the WL. The wind would have the same difference going both ways would it not? Take away 2 eggs .. give back 2 eggs. Something tells me it can't be so though. Don't know what the something is though. I think in reality it has to do w something being not linear. Like the headwind would increase the drag more than the tailwind would reduce it????

manyboats said:

"but going one way into it is often compensated for by going with it at some point."

To me the question is to what extent.

I don't see how bucking wind and then going w it could work out to be a plus. But if there was no current and the wind was the same going both ways at the same speed it would seem to average out. If one went the same speed the resistance of the boat would remain the same below the WL. The wind would have the same difference going both ways would it not? Take away 2 eggs .. give back 2 eggs. Something tells me it can't be so though. Don't know what the something is though. I think in reality it has to do w something being not linear. Like the headwind would increase the drag more than the tailwind would reduce it????

Click to expand...

No plus....but the delta is probably so small and unpredictable most of us don't care...

Water is about 800 times harder to push aside than air.

It takes 17K for the breeze to represent 1 LB per sq ft of resistance., so unless you have a bif wind or a bloat boat , pushing water into waves is where much of the energy goes.

manyboats said:

Daddyo,
Lets see a good pic of your aft end. Perhaps I'm wrong but every DeFever I've seen is semi-disp without a doubt but there was a smaller (34' ?) DeFever that surprised me re her lines aft. A Krogen 42 has almost no submerged transom and is clearly a full disp boat. I'd rather not go into the Buttock Line stuff as some here don't like it but it is the best way to define a full disp hull in the aft end. Let's see what you've got.

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Sorry to be so late on this. If you look at the round deep bilge well aft and the taper at the stern will see what I mean. This boat is far more displacement then semi. There just isn't the flat aft sections for lift. Pics are of a sistership.

Daddyo, thanks for posting those pics of the floscan. Very interesting.

Daddyo,
Yes now that I can see your QBBL fairly well and your emersed transom. The DeFever is definitely semi disp and a bit closer to full disp than an Island Gypsy that I think (hull shape wise) is on the other side of SD. As is many to most other trawlers on the forum.
I see on the top pic the chine is straight (or parallel to the WL) as would be the case w a full plaining hull at rest. With the DF your inner buttock line (where bottom meets the keel) has a rather steep angle for trawlers. So your boat is a semi-disp and a bit closer to FD.
For years I've seen the submerged straight chine aft and in my own mind labeled the DF a SD boat. But quite a few guys obviously haven't liked that so I'm glad you pulled that out in the open. The DF is closer to FD.

Here is a full blown full disp hull. You can see that the QBBL running fore and aft half way between the keel and the side of the boat is very steep. Could be about 30 degrees.

I made a little sea trial and my port engine heated up and busted a hose. I stopped it and continuous with just one engine and the speed was almost the same with half consumption.

Sergio "Alemao" Sztancsa, Sent from my iPhone using Trawler

manyboats said:

Daddyo,
Yes now that I can see your QBBL fairly well and your emersed transom. The DeFever is definitely semi disp and a bit closer to full disp than an Island Gypsy that I think (hull shape wise) is on the other side of SD. As is many to most other trawlers on the forum.
I see on the top pic the chine is straight (or parallel to the WL) as would be the case w a full plaining hull at rest. With the DF your inner buttock line (where bottom meets the keel) has a rather steep angle for trawlers. So your boat is a semi-disp and a bit closer to FD.
For years I've seen the submerged straight chine aft and in my own mind labeled the DF a SD boat. But quite a few guys obviously haven't liked that so I'm glad you pulled that out in the open. The DF is closer to FD.

Here is a full blown full disp hull. You can see that the QBBL running fore and aft half way between the keel and the side of the boat is very steep. Could be about 30 degrees.

Click to expand...

How about hard chine full displacement

Daddyo said:

How about hard chine full displacement

Click to expand...

A box is full displacement...ask any tugboat captain..

After I fixed and went back home I asked a mechanic that his Phone is 3208 and I asked him if I could don`t use the turbos, twice 210Hp are enough for 8.5 knots and the consumption could be low.